1. Technical Field
The present invention relates generally to electronic packages, and more particularly, to an electronic package including an elastomeric member that supports a substantial portion of the load of a heat sink.
2. Related Art
Current electronic packages are built with semiconductor chips or devices that are exposed so that an end user can connect a heat sink to the chip without additional thermally resistant layers. The chips may be encapsulated or have a layer of material about the chip. In many cases, the chips are flipped and connected with a ball grid to a substrate.
One problem with this arrangement is that users can damage the chip when they attach the heat sink. One effort to remedy this problem is the use of a ring around the chip that is lower than the chip to guide the heat sink into position. This procedure, however, still may cause damage to the chip when the heat sink meets the chip. In addition, once the heat sink is in position, it needs to be held on with enough force to remain in contact with the chip. Most of the heat sink load is still on the chip with this configuration. The heat sink load includes not only the weight of the heat sink, but also the force of the coupling mechanism, e.g., spring clips, used to connect the heat sink to the substrate and any shock or vibration experienced during use.
Another problem relative to attaching chips and heat sinks is that new chip technology is advancing with chips that have internal structures that are more fragile than in the past. For instance, one new chip technology provides a dielectric inside the chip such that it includes an outer glass like material with an organic and softer, inner material. These chips cannot withstand the heat sink load as well as older chip technology. Hence, when a heat sink is forced into contact with a new chip, the heat sink load can more easily damage the chip.
The above-described problem is magnified in that the new chips give off more heat and, therefore, require larger and heavier heat sinks than predecessor chips. This is the case even though the new chips are smaller. New chips also have different coefficients of thermal expansion (CTE) than current heat sinks, which also increases the stresses experienced by the new chips.
One mechanism that has been used to protect chips is adding a lid over the chip. The lid is oftentimes attached to the chip with an adhesive. A lid, however, adds another layer to the package and, hence, thermal resistance, which negatively impacts performance and reliability. Further thermal resistance is created when an adhesive layer is used to attach the lid to the chip. Another problem with the use of lids is that users want to be able to add the heat sink to the package and then conduct testing. In many cases, the heat sink is also attached to the lid with an adhesive. If the package does not work, the user must then remove the heat sink and/or the lid. Since the heat sink and lid are adhered in place, the user must overcome the adhesive force to remove the heat sink and/or the lid, which can damage the chip.
Another effort to solve the chip protection problem includes using an adhesive guard applied to the substrate around the chip. The adhesive guard is applied by the user at the time of final mechanical assembly of the finished product. This has solved some of the damage that occurred from that point on but has had no impact on damage occurring sooner in the process. In addition, this solution was not implemented so as to support any significant portion of the heat sink load in operation. Hence, the chip is still susceptible to damage during use.
In view of the foregoing, there is a need in the art for an electronic package having a mechanism to place a heat sink in contact with a chip but not support the heat sink load on the chip.
The invention includes an electronic package having an elastomeric member that supports a substantial portion of the load of a heat sink. The elastomeric member includes portions that are compressible to different degrees. The invention allows larger heat sinks on smaller and more fragile chips, and protects the chips from damage.
A first aspect of the invention includes an electronic package comprising: a substrate having a first portion and a second portion; a semiconductor chip positioned on the first portion; and an elastomeric member positioned on the second portion, wherein the elastomeric member supports a substantial portion of a heat sink load.
A second aspect of the invention is directed to an electronic package comprising: a substrate having a first portion and a second portion; a semiconductor chip positioned on the first portion of the substrate; an elastomeric member positioned on the second portion of the substrate; and a heat sink positioned on the semiconductor chip and on the elastomeric member, wherein the elastomeric member supports a substantial portion of a load of the heat sink to prevent damage of the semiconductor chip.
A third aspect of the invention is directed to a method of constructing an electronic package, the method comprising the steps of: providing a substrate; coupling a semiconductor chip to the substrate; placing an elastomeric member having portions compressible to different degrees adjacent the semiconductor chip; and coupling a heat sink to the substrate such that a substantial portion of a load of the heat sink is supported by the elastomeric member.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.